I measured the Burson HA-160 using a M-Audio ProFire 610 Firewire sound interface with Spectra Plus FFT analysis software. I used both 100 ohm and 500 ohm resistors as a loads, with the volume setting trimmed to produce a 1V p-p output level. Measurements were made with 24 bit, 192 kHz sampling and 96 kHz audio bandwidth, and the frequency response of the 610 was corrected using a loopback measurement. The forest of low level spurs in the single tone measurements results from pickup from the air due to the unshielded load resistor connected to the test leads with alligator clips.

Total harmonic distortion plus noise (THD+N) was measured with a 1 kHz test tone into both the 100 ohm and 500 ohm loads. Into 100 ohms, the result was 0.015%, while into 500 ohms, the result was a bit less (0.011%). This is preamp level distortion as youâ€™d expect.

THD+N versus frequency was pancake flat into both loads up to the point where the anti-aliasing filter kicked in near 96 kHz.

Intermodulation distortion, measured with a pair of tones at 7 kHz and 60 Hz, was virtually unmeasurable. Spectra Plus says 0.0009% for both loads, but that is below the level that I trust the test equipment to measure.

Test tones at 19 and 20 kHz produce a 1 kHz intermodulation product 100 dB down from the fundamental tones.

Frequency response is also flat as a board into both loads, but level is higher into the lower impedance load with the same volume setting.